This relates generally to graphics processing.
Shading is a process of applying lighting effects to an object to be depicted. Deferred shading is a popular way of rendering a scene where rendering is performed after the visibility is resolved. Specifically shading is deferred until occlusions have been resolved. Typically this is done in two passes. The first pass writes out inputs required for shading (surface normal, depth, view vector, etc.) into a buffer called the geometry buffer. The second pass is a full screen pass or a compute shader pass where shading calculations are done. One advantage of deferred shading is that only visible surface fragments are shaded. Shading is deferred until all geometry processing is complete.
Graphics systems consume a large amount of power in battery-powered applications in which low power usage is advantageous. Examples of devices that are battery powered include cell phones and tablets. It is crucial to reduce the power consumption to increase battery life.